The “impossible trinity”
Diseases originating from narrow channels within the body, such as natural orifices, the cardiovascular system, and the cerebrovascular system, pose significant global health challenges, contributing to approximately 25 million annual deaths, and ranking among the top 10 causes of death worldwide according to the World Health Organization (WHO)[1]. Up to date, interventional surgery, which offers reduced invasiveness, shorter recovery times, and higher success rates compared to traditional open surgery, has become a cornerstone in clinical practice[2][3].
Intervention procedures are typically executed in one of two ways: either through the direct advancement of a micro-catheter into the affected area via narrow channels, or by initially introducing a slender guidewire, followed by the delivery of a catheter equipped with surgical tools[4]. However, these established methods encounter several challenges. Firstly, the fixed pre-shaped bending contour restricts inflexibility, posing difficulty when navigating through tortuous blood vessels, especially those with sharp turns. Secondly, manual intervention places substantial demands on the surgeon, who must maintain stable manipulation of surgical tools while simultaneously monitoring feedback from the medical imaging system for navigation. Improper manipulation by an inexperienced interventionalist can lead to patient discomfort or, in severe cases, vessel perforation[5], resulting in irreparable medical accidents.
To address these challenges, slender robots, commonly referred to as small-scale continuum robots, have been proposed to automate the navigation of catheters or guidewires, owing to their narrow cavity-accessing ability, bringing superiorities of quick recovery, and low infection risk. However, despite the small continuum robots bring promising prospects of small contour, precise steering, and visualized treatment, it remains a great challenge for a robot can have all these three significant specifications at the same time, resulting in an “impossible trinity” and therefore hindering its further diagnosis and treatment inside bodily narrow pathological areas.
Our proposal of fiberscopic robot
Recognizing the advantages of optical fiber in small-scale and media transmission applications, we introduced a design for a submillimeter-scale soft continuum robot that utilizes an optical fiber array. By leveraging the light transmission properties of the fibers, we anticipate that this robot could perform endoscopic imaging. Additionally, to enable active steering of the robot, we propose incorporating the magnetic spray technology from our previous research[6], which allows inanimate objects to be transformed into millirobots with minimal changes to their size. With further miniaturization for integrating in situ surgical operations, we believe that this impossible trinity could potentially be unraveled.
Prototype verification
Based on the aforementioned idea, the developed fiberscopic robot mainly consists of an optical fiber array for imaging, a customized tool for implementing treatment, a hollow skeleton for deploying fibers/tool, and a functionalized skin for controlling. The submillimeter hollow skeleton is obtained by micro-scale 3D printing. With a central fiber bundle and several circular deployed light guide fibers, the capacity of in situ imaging can be utilized for disease diagnosis. Besides, by embedding a laser fiber or micro-tube, the laser or fluidic drug can then be delivered to the pathological target, carrying out the visualized treatment. To control the motion of the probe precisely, we proposed the strategy of functionalized skin. Firstly, a layer of magnetic elastomer was covered on the surface by employing magnetic spray, granting the probe active steering capacity under a magnetic field while keeping almost no increase in its contour. Then, a layer of hydrogel skin was further coated on the outer surface of the robot body to create the hydrophilic characteristic to reduce the potential friction during the intervention process. Consequently, a functionalized submillimeter probe robot with a 950 μm diameter was achieved with active navigation and in situ treatment simultaneously, unraveling the “impossible trinity” (Fig.1).
Fig. 1: Overview of the optical fiber-based sub-millimeter continuum robot with imaging, maneuvering, and medical operation capabilities.
Through in vitro experiments conducted within a bronchial tree phantom and ex vivo trials using porcine lung models, we successfully demonstrated the robot's ability to navigate within confined spaces, perform high-precision scanning imaging, and carry out various in situ biomedical procedures for pathological areas. These results highlight the significant potential of the proposed fiberscopic robot for clinical applications.
Implications for Future Research
The fiberscopic robot exhibits superior performance in interventional procedures that surpasses the capabilities of existing continuum robots. Striving for practical application, we aim to further optimize the design and control of the fiberscopic robot, prioritizing safety and reliability during interventional surgery. Moreover, we look forward to implementing in vivo trials to showcase the performance of the fiberscopic robot in clinical scenarios.
This research provides a significant solution for the development of a clinical surgical robot aimed at achieving early diagnosis and therapeutic goals in more hard-to-reach bodily regions. With continuous technological advancements, it is believed that the fiberscopic robot will make greater contributions to human health in the foreseeable future.
References
- The top 10 causes of death, <https://www.who.int/news-room/fact-sheets/detail/the-top-10-causes-of-death> (2020).
- YANG, G.-Z. et al. The grand challenges of Science Robotics. Rob. 3, eaar7650 (2018).
- Cianchetti, M., Laschi, C., Menciassi, A. & Dario, P. Biomedical applications of soft robotics. Rev. Mater. 3, 143-153 (2018).
- Ivar Seldinger, S. Catheter replacement of the needle in percutaneous arteriography: a new technique. Acta Radiol. 49, 47-52 (2008).
- Khasawneh, F. A. & Smalligan, R. D. Guidewire-Related Complications during Central Venous Catheter Placement: A Case Report and Review of the Literature. Case Rep Crit Care 2011, 287261 (2011).
- Yang, X. et al. An agglutinate magnetic spray transforms inanimate objects into millirobots for biomedical applications. Rob. 5, abc8191 (2020).